Tentative hydrolysis

Figure 3. Tentative hydrolysis mechanism of different xylans by the xy-lanolytic enzymes of T. rtesei.

Volume V (Tentative) Hydrolysis (Sulfate Esters, Carboxyl Esters, Glycoside Bonds), Phosphoro/ysis, and Hydration... 

Chlorphenylid, Flucofuron and Sulcofuron Waters (Tentative Methods based on methylation and GC-ECD, ion-pair HPLC and hydrolysis of Sulcofuron to 4-chloro-3-trifluoromethylaniline by GC-ECD), 1993... 

The detection of microgram quantities of pyrethrins, cinerins, keto alcohols, and chrysanthemum acids by paper chromatography and by application of these techniques to a study of possible metabolites enabled certain tentative conclusions that imply hydrolysis in insects of a large portion of the radioactive pyrethrins and synergists to corresponding keto alcohols and chrysanthemum acids. 

Soil Benzidine was added to different soils and incubated in the dark at 23 °C under a carbon dioxide-free atmosphere. After 1 yr, 8.3 to 11.6% of the added benzidine degraded to carbon dioxide primarily by microbial metabolism and partially by hydrolysis (Graveel et al, 1986). Tentatively identified biooxidation compounds using GC/MS include hydroxybenzidine, 3-hydroxybenzidine, 4-amino-4 -nitrobiphenyl, A(A -dihydroxybenzidine, 3,3 -dihydroxybenzidine and 4,4 -dinitrobiphenyl (Baird et al, 1977). Under aerobic conditions, the half-life was estimated to be 2 to 8 d (Lu et ah, 1977). 

Chemical/Physical. Endosulfan detected in Little Miami River, OH was readily hydrolyzed and tentatively identified as endosulfan diol (Eichelberger and Lichtenberg, 1971). Undergoes slow hydrolysis forming the endosulfan diol and sulfur dioxide (Worthing and Hance, 1991). The hydrolysis half-lives at pH values (temperature) of 3.32 (87.0 °C), 6.89 (68.0 °C), and 8.69 (38.0 °C) were calculated to be 2.7, 0.07, and 0.04 d, respectively (Ellington et al., 1988). Greve and Wit (1971) reported hydrolysis half-lives of P-endosulfan at 20 °C and pH values of 7 and 5.5 were 37 and 187 d, respectively. In a 1 pM sodium bicarbonate buffer solution at pH 8.15 and 28 °C, suspensions of sea sand, titanium dioxide, a-ferric oxide, a-FeOOH, laponite, and silicon dioxide catalyzed the hydrolysis of a-endosulfan to endosulfan diol. The uncatalyzed hydrolysis rate constant and half-life was 4.01 x lO Vsec and 0.20 d, respectively (Walse et al., 2002). 

Unfortunately, there is presently only a very tentative bit of evidence available to substantiate this prediction. In one experiment at an acid pH, the overall rate of hydrolysis of the n-octyl ester of 2,4-D was measured in a sediment/water slurry in which a substantial fraction of the ester was sorbed. The rate was observed to be substantially faster than the predicted aqueous phase rate. Though this is an indication that the above prediction is correct, much more experimental work is needed to substantiate and quantify this predicted rate enhancement. 

Lipases generally show low hydrolytic activity when their ester substrates are dissolved in aqueous media and present in imimeric form. A pronounced increase in activity is observed when the substrate concentration reaches the solubiUty limit and a separate phase is formed. In the case of surfactants this impUes that a possible increase in activity can be expected above the CMC. Attempts to investigate how the hydrolysis is affected by micelUzation were made for the linear surfactant 1 of Fig. 4. The CMC of this surfactant is 10 mM, and a marked change in the activity of the MML is indeed observed when this concentration is exceeded, see Fig. 6. The initial reaction is faster (steeper slope) above the CMC. When CALB was used to catalyze the reaction, no increase of the reaction rate was observed above the CMC. It was also found that the rate, expressed in moles of surfactant consumed per minute, was independent of the start concentration (same slope). A tentative explanation to the fact that the MML but not the CALB-catalyzed hydrolysis is accelerated by the presence of micelles may be that MML but not CALB is able... 

Weinblum and Johns43 also have shown that hydrolysis of the two dimeric dinucleotide products, D1 and Dz, leads to the isolation of two forms of thymine dimer which were assigned tentatively to structures 10 and 11. 

Allylzinc bromide is able to add to a variety of alkenyl Grignard reagents in THF at 35 °C123. The structure of the hydrocarbons 184, obtained in moderate yields after hydrolysis (due to their volatility), suggested that 1,1-dimetallic species tentatively formulated as 185 were regioselectively formed (equation 89). Additional examples were subsequently reported but the scope of this intriguing reaction remained rather unexplored and the reactivity of 185 towards various electrophiles was not investigated124,125. 

It has been recently reported (109) that use of both Penase and lactamase II hydrolysis and screening assays prior to chromatographic analysis can tentatively classify -lactams into three subgroups the first group includes a ceftiofur metabolite represented by desfuroyl-ceftiofur-cysteine the second, cephapirin and the third, penicillin G, ampicillin, amoxicillin, and cloxacillin. In this approach, portions of aqueous extracts of tissues are treated separately with Penase and lactamase II, and results are compared with those of untreated samples and positive controls. Bioactive ceftiofur metabolites are present, provided that the extracts retain inhibitory activity after Penase treatment but lose activity after lactamase II treatment and are positive in response to the immunochemical Lac-Tek-Cef test but negative to the Lac-Tek-Bl test (113). This approach can eliminate a large number of negative samples and, therefore, increases the efficiency of the assay. 

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